4.3 Monitoring Bti toxin resistance in natural populations
Resistances to Cry toxins are known to appear rapidly in
Lepidopteran or Dipteran species when Bt treatments not
containing Cyt toxins are applied.29,30 In the present work it is
shown that multiple resistances to Cry toxins in the mosquito
Ae. aegypti can arise rapidly, even in the presence of Cyt toxins.
In most studies investigating the emergence of resistance to Bti
treatment in laboratory or under field conditions, only resistance
to the complete Bti toxin mixture has been investigated.23 – 25,27
The resistance ratio to commercial Bti observed in these studies
is usually of the same order of magnitude as the RR50 observed
for the LiTOX strain (2–3-fold resistance),22,23,61 suggesting that
much higher resistance to individual toxins may have actually
evolved in the populations tested. Considering that resistance to
Cry toxins might act as a first step to resistance to full Bti toxin
mixture, the present results highlight the importance of testing
for each toxin individually in order accurately to monitor Bti toxin
resistance evolution in field populations.